1. Field of the Invention
The present invention relates in general to automotive automatic transmissions, and more particularly to a drum supporting structure installed in the automatic transmission for rotatably supporting a drum on a drum support. More specifically, the present invention is concerned with drum supporting structures of a type which has a well-balanced construction throughout the entirety thereof to suppress undesired inclination thereof.
2. Description of the Prior
As is known, in an automotive automatic transmission, there is arranged a drum supporting structure that comprises a drum support on which a drum is rotatably supported. Within the drum, there is installed a hub, and between the drum and the hub, there is arranged a friction element. When the friction element is in ON (viz., engaged) condition, power transmission is carried out between the drum and the hub, while, when the friction element becomes OFF (viz., disengaged) condition, the power transmission is suppressed.
In order to clarify the task of the present invention, one conventional drum supporting structure will be described with reference to FIG. 15 of the accompanying drawings. The structure of the drawing is described in Japanese Patent First Provisional Publication 61-38261.
In FIG. 15, there is shown a rear view of a circular wall portion of a drum support 50 used in the drum supporting structure of the publication. As shown, a plurality of hydraulic fluid passages 52 are provided at a lower part of the circular wall portion of the drum support 50, which feed a hydraulic fluid to hydraulic fluid passages 54 provided at a central portion of the drum support. On an upper part of the circular wall portion of the drum support 50, there are integrally provided radially extending ribs 56 for reinforcement of that upper part. At a piston supporting portion 58, there is arranged a piston (not shown) of a friction element. Behind the piston, there is defined a fluid working chamber for the piston. Although not shown, a drum is coaxially and rotatably supported on a cylindrical hollow shaft portion of the drum support 50. (The entire construction of the drum support 50 is easily understood when referring to FIG. 14.)
However, the drum support 50 disclosed by the publication fails to exhibit a well balanced construction therethroughout due to an imbalanced arrangement of the structures such as the hydraulic fluid passages 52 and ribs 56 provided on the circular wall portion of the drum support 50. That is, in the drum support 50, the rigidity of the lower part of the circular wall portion is extremely different from that of the upper part of the same. As is known, if such ill-balanced drum support 50 is practically used in the transmission, undesired inclination of the drum support 50 relative to the bolted lower part tends to occur. This phenomenon becomes much severe when the lower part of the circular wall portion of the drum support 50 is secured to the transmission case by bolts 60, as shown.
It is therefore an object of the present invention to provide a drum supporting structure for an automotive automatic transmission, which is free of the above-mentioned drawback.
According to a first aspect of the present invention, there is provided a drum supporting structure for use in an automatic transmission including a transmission case, a drum rotatably installed in the transmission case and a friction element incorporated with the drum. The drum supporting structure comprises a drum support immovably installed in the transmission case, the drum support including a cylindrical hollow shaft portion on which the drum is rotatably disposed and a circular wall portion which is concentrically and integrally formed on one end of the cylindrical hollow shaft portion; a first part of the circular wall portion, the first part being secured to the transmission case and having a plurality of hydraulic fluid passages defined therein; and a second part of the circular wall portion, the second part having a plurality of blind bores defined therein, the number of the blind bores being at least the same as that of the hydraulic fluid passages, the first and second parts being provided at diametrically opposed portions of the circular wall portion and the blind bores extending toward the extension of the hydraulic fluid passages.
According to a second aspect of the present invention, there is provided a drum supporting structure for use in an automatic transmission including a transmission case, an output shaft rotatably installed the transmission case, a drum rotatably disposed around the output shaft, a first friction element incorporated with the drum and a second friction element arranged behind the drum. The drum supporting structure comprises a drum support immovably installed in the transmission case and having a through bore through which the output shaft passes, the drum support including a cylindrical hollow shaft portion on which the drum is rotatably disposed and a circular wall portion which is concentrically and integrally formed on one end of the cylindrical hollow shaft portion, the circular wall portion having a rear surface that faces the second friction element; a first part of the circular wall portion, the first part being bolted to the transmission case and having a plurality of hydraulic fluid passages defined therein; and a second part of the circular wall portion, the second part having a plurality of blind bores defined therein, the number of the blind bores being at least the same as that of the hydraulic fluid passages, the first and second parts being provided at diametrically opposed portions of the circular wall portion and the blind bores extending the extension of the hydraulic fluid passages.